1. Field of the Invention
The present invention relates to a film feed apparatus for detecting the feed speed of a film having perforations, and a camera.
2. Related Background Art
A conventional method of recording data on a magnetic layer (magnetic recording portion) formed on a film will be described below with reference to FIG. 6.
Referring to FIG. 6, a film 17 has a magnetic recording portion 17d. This film also has perforations 17b, each indicating the start position of a corresponding exposure surface 17a, and perforations 17c, each indicating the end position of a corresponding exposure surface 17a. Photosensors 14a and 14b are used to detect the perforations 17b and 17c. A magnetic head 12 is positioned to oppose the magnetic recording portion 17d.
The magnetic head 12 is used to magnetically record photography information such as the date of photography, the print aspect ratio, and exposure information on the magnetic recording portion 17d during film feed. In this case, in order to properly perform a magnetic recording operation by detecting the moving speed of the film, a write frequency for magnetic recording is determined at the start of film feed.
FIG. 7 is a timing chart of a one-frame film feed operation and a magnetic recording operation, showing the relationship between the perforations 17b and 17c detected by the photosensors 14a and 14b.
Referring to FIG. 7, when film feed is started, the perforation 17c is detected first by the photosensor 14b. The passing time of this detected perforation 17c is measured to detect the feed speed of the film. A proper write frequency for magnetic recording is determined from the detected feed speed, and a magnetic recording operation using the magnetic head 12 is started. The magnetic recording operation is terminated before the perforation 17c is detected by the photosensor 14a, and film feed is stopped at the end of detection of the perforation 17b.
Letting L be the length of each perforation, and t be the passing time of the perforation 17c which is detected and measured by the photosensor 14b, a feed speed v is given by: EQU v=L/t
Letting D be the recording density indicating the number of data written on the magnetic recording portion 17d per unit length, a magnetic recording frequency f is given by: ##EQU1##